As one example of continuously variable transmission, a transmission, which is constructed to clamp a power roller between a pair of discs arranged opposed to each other is known. The portion of the pair of discs where an outer circumferential side from a predetermined radius has an arcuate plane of a predetermined radius as cut in a plane on the center axis. On the other hand, the power roller is a disc-shaped member, and its sectional figure along the in-depth direction of the outer circumferential portion is congruent with the arcuate figure of the opposed face of the discs. The power roller is clamped in between a pair of the discs, and the power roller is rotated by rotating one of the discs, and the other disc rotates sequentially. Then, the power roller is inclined to move the radial position of the contact portion against one of the discs, i.e., the radial position from the center axis of the disc outward, and also to move the radial position of the contact portion against the other disc to inner circumferential side, so that the speed change ratio corresponding to the proportion of the radii of each contact portions is thereby set.
In the toroidal type continuously variable transmission, a torque is thus transmitted between a pair of discs through the power roller. However, if the transmission of the torque is executed by a frictional force between the disc and the roller, abrasion of a frictional contact portion is rather hard and become unable to use precociously. Therefore, according to the prior art, the construction is made to form an oil film between the power rollers and the discs, and transmit the torque by a shearing force of the oil film. One example of the devise for feeding lubricating oil is disclosed in Japanese Patent Laid-Open No. 10-132047.
The construction disclosed in this Laid-Open will be described briefly hereafter. There is provided a roller holding member, which is shaped to clamp the power roller from both top and bottom sides, and the power roller is held by the roller holding member in a rotatable condition. The roller holding member is connected to a piston rod of a linear acting type hydraulic cylinder through a ball joint, and an oil passage for feeding the lubricating oil is formed inside of the piston rod and the roller holding member. And the leading end portion of the oil passage opens to the position opposed to the outer circumferential face of the power roller at the roller holding member. Accordingly, an oil pressure is generated by a hydraulic pump driven by a power source such as an engine, under the status such that the power source is operated to rotate the disc with inputting the torque to the disc of input side. As a result, the lubricating oil fed by a pressure through the oil passage is blown to the outer circumferential face of the power roller. The lubricating oil thus adhered on the power roller is fed to the contact portion against the disc and the oil film is thereby formed consequently.
As mentioned above, generally, the lubricating oil is fed compulsorily according to the prior art. Accordingly, when the torque is being inputted to the continuously variable transmission and the continuously variable transmission is thereby rotating, the hydraulic pump is driven simultaneously to feed the lubricating oil to the continuously variable transmission sufficiently. However, in case the continuously variable transmission is not used, i.e., when the rotation is halted, the hydraulic pump for feeding the lubricating oil and the lubrication system is halted. Because it is not only unnecessary to feed the lubricating oil, but also motivity is wasted unnecessarily. Accordingly, if the continuously variable transmission is left in the halt condition for a long time, following troubles may occur, such as; difluent of the lubricating oil from the rolling face of the power roller or the disc due to absence of the lubricating oil; disappear of the oil film due to evaporation; and shortage of the lubricating oil.
If the torque is inputted to the continuously variable transmission by starting the power source in spite of occurrence of such troubles, there is a possibility of occurring breakage of the oil film on the rolling face and causes abrasion such as adhesive wear on the power roller and the disc. That is, in the driving mechanism wherein the continuously variable transmission is directly connected to the power source such as an engine, the continuously variable transmission is rotated by being inputted the torque simultaneously with starting up of the engine, and transmission of the torque is executed between the power roller and the disc. Moreover, although the hydraulic pump is driven by the power source at the same time, the time lag is generated until the hydraulic oil is substantially fed, because of the absence of the oil from the hydraulic pipeline due to long term period of the halted condition, or because of the required time for saturating the oil in the oil passages. Accordingly, the power roller and the disc have to rotate without the oil film, or with shortage of the lubricating oil on its rolling face for a certain time from the start up. As a result, the breakage of the oil film is occurred and cause direct contact between the power roller and the disc. Therefore, there is a possibility for the continuously variable transmission to be out of order due to the abrasion at the contact portion between the power rollers and the discs.
This invention has been conceived in the view of the aforementioned technical problem and its object is to provide a lubrication device for a toroidal type continuously variable transmission which can certainly maintain the oil film by feeding the lubricating oil to the contact portion between the rolling members even when it is started up.